(recirculation to pumping station) is needed.
11. Whether plant is to be of aboveground or
belowground construction.
12.
Seismic loading (if necessary).
13.
Electric power characteristics for motors.
14. Whether automatic operation of air lift pumps
should be required.
15. Wind load and ice load for rotating sludge
collector.
16. Organic loading (5-day BOD) if other than that
given in the text.
17. Total suspended solids if other than given in
the text.
18. Size of hypochlorite mixing tank if larger
capacity than 113.4 L 30 gallons is needed.
19. Size of hypochlorite solution tank if larger
capacity than 208 L 55 gallons is needed.
20. Whether, for extended aeration type plant,
eventual conversion to step aeration type is
anticipated.
For plants below 0.66 L/s 15,000 GPD capacity,
hopper bottom only should be specified for settling
tanks. For plants above 4.38 L/s 100,000 GPD
capacity, mechanical sludge collectors only should
be used in settling tanks. For plants between 0.66
L/s and 4.38 L/s 15,000 and 100,000 GPD capacity,
either hopper bottom or mechanical sludge collector
should be allowed as a Contractor's option.
However, of the various types of mechanical sludge
collectors, rotating sludge collectors appear to be
available for plants of 1.31 L/s 30,000 GPD and
above; chain-and-flight, 1.75 L/s 40,000 GPD and
above; traveling reciprocating type, 0.66 L/s 15,000
GPD and above.
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The equipment shall be chain-and-flight type, designed to move settled
sludge to a sludge hopper. The equipment shall include a drive assembly
and a sludge collector assembly.
a.
Design: The sludge collector assembly shall operate at a linear
speed between 10 and 15 mm per second 2 and 3 fpm. The mechanism
and its component parts shall be designed, with a minimum factor
of safety of 4, to withstand all structural and mechanical
stresses brought about by the drive assembly and the following
loadings: dead load and a sludge load equal to a horizontal load
of 117 N per meter 8 lbs per linear foot of scraper blade in a
scraping position. The mechanism shall be designed for continuous
SECTION 11375N
Page 45
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